Hydrogen chloride is often found in gas streams generated during industrial processes and is commonly found in off-gases or waste gases from other sources such as incinerators. For example, while the concentration of hydrogen chloride in the flue gas from municipal incinerators is usually less than 200 ppm, in some cases such as department store incinerators the concentration is as high as 2,000 ppm. A common source of HCl in gas streams is the incineration of industrial or municipal waste containing PVC plastics (polyvinyl-chloride); in fact, it is expected that the PVC waste content in municipal waste will double between the years 1975 and 2000. It is desirable and almost necessary that the hydrogen chloride be removed from these gas streams both because of the toxic nature of the HCL and to avoid pollution and because of the corrosive nature of HCL which poses problems in any off-gas cleanup system. It is recognized that corrosion by HCL is one of the major problems in waste incineration, corrosion by hydrogen chloride being an especially serious problem if water condenses anywhere in the system.
One particular area where polyvinyl-chloride plastics have posed a serious problem is in the disposal of low specific activity transuranic wastes (LSA wastes), as PVC plastics constitute approximately 40% of the LSA wastes. The LSA wastes generated at the various sites at which work in the area of nuclear energy is conducted have in the past been disposed of in land burials. These wastes at present are being placed in above-ground storage at the Idaho National Engineering Laboratory located in southeastern Idaho pending determination of what and where a national transuranic waste repository shall be.
These wastes, typically composed of paper, plastic and metal refuse, are contaminated with minute quantities of alpha-emitting elements. While the hazard of direct radiation from this waste is insignificant, ingestion or inhalation of the toxic elements is extremely dangerous. Therefore, properly controlled disposal of such wastes is necessary to meet Federal standards as well as to protect the environment. Because of the volume of this waste generated annually, space for the controlled disposal is at a premium. Consequently, it is highly desirable to reduce the waste volume by compaction or incineration which produces a noncombustible waste. This is important for two reasons: (1) it is believed that when a national repository is defined, it will accept only noncombustible material; and (2) several of the waste contaminants (plutonium. zirconium, beryllium) are pyrophoric. Incineration reduces the fire hazards for engineered storage.
While incineration provides an attractive method for reducing the waste volume, in view of the high PVC plastic composition of the waste, corrosion of the flue gas duct work is a significant problem. Two possible courses of action are available to eliminate or substantially reduce the problem of hydrogen-chloride corrosion of the off-gas duct work. The PVC plastics can be segregated from the waste going to the incinerator or the hydrogen chloride produced by the incineration can be neutralized before it causes extensive corrosion. In terms of efficiency and expense, the second choice is clearly more practical.
Although the hydrogen chloride could be removed from the off-gases by wet-scrub techniques since wet-scrub equipment and processes are reasonably well developed for industrial applications, a liquid waste would be generated by this method and in application of this to the incineration of LSA waste, this liquid waste would have to be solidified for the control of the radioactivity. This, of course, would require additional equipment consequently raise operating costs and difficulties.
Another potentially attractive method for hydrogen chloride abatement involves reacting the hydrogen chloride with ammonia. However, past methods employing ammonia have posed problems as there was no convenient or satisfactory method for collecting the ammonium chloride which was formed.
It is an object of the present invention to provide a method for the removal of hydrogen chloride from gas streams.
It is another object of the present invention to provide a method for removing hydrogen chloride from the off-gases generated during the incineration of polyvinyl-chloride plastics.
A specific object of the present invention is to provide a method for removing hydrogen chloride from the off-gases produced during the incineration of radioactive contaminated polyvinyl-chloride plastics, which method provides for removal of the hydrogen chloride without generating large volumes of liquid wastes.